Method of inserting a flexible preform in a mold

ABSTRACT

A method for inserting a flexible, oversized preform into an opening in a hollow mold is disclosed. The oversized preform is initially formed so as to have a configuration similar to that of the interior surfaces of the mold. The cross sectional size of the preform relative to the mold is temporarily reduced by forming an inwardly projecting furrow in the preform so that the preform may be inserted into the mold. An assembly for inserting the preform into the mold and reducing the cross sectional size of the preform as it is inserted into the mold is also disclosed.

United States Patent Wiltshire 1 July4, 1972 [54] METHOD OF INSERTING AFLEXIBLE PREFORM IN A MOLD [72] Inventor: Arthur J. Wlltshire,Cleveland, Ohio [73] Assignee: Structural Fibers, lne., Chardon, Ohio[22] Filed: Feb. 4, 1970 [21] Appl. No;: 8,670

[52] US. Cl. ..29/451, 29/235 [51] Int. Cl...... [58] Field of Search...29/235, 451, 523

[56] mm, Cited UNITED STATES PATENTS 1,074,505 9/1913 Kempshall ..29/523UX 2,977,994 4/1961 Xenis .i ..29/451UX 3,145,464 8/1964 Green ..29/235XPrimary Examiner-Charlie T. Moon Attorney-McNenny, Farrington, Pearne &Gordon [57] ABSTRACT A method for inserting a flexible, oversizedpreform into an opening in a hollow mold is disclosed. The oversizedpreform is initially formed so as to have a configuration similar tothat of the interior surfaces of the mold. The cross sectional size ofthe preform relative to the mold is temporarily reduced by forming aninwardly projecting furrow in'the preform so that the preform may beinserted into the mold. An assembly for inserting the preform into themold and reducing the cross sectional size of the preform as it isinserted into the mold is also disclosed.

7 Claims, 3 Drawing Figures METHOD OF INSERTING A FLEXIBLE PREFORM IN AMOLD BACKGROUND OF THE INVENTION This invention relates generally to themolding of fiber-reinforced, plastic articles, such as tanks or thelike, wherein a fiber preform is subsequently impregnated with plasticmaterial. More particularly, a novel and improved method and assemblyfor inserting a flexible, oversized preform into a mold are disclosed.

Although this invention is concerned with the molding offiber-reinforced plastic articles generally, it will be discussed hereinwith particular reference to the molding of fiber-reinforced plastictanks.

PRIOR ART In the molding of fiber-reinforced, plastic articles such astanks, one commonly used method includes initially forming a hollowpreform. In the case of fiber-reinforced, cylindrical tanks, the preformincludes a tubular sidewall portion having an integrally formed end wallat one end. The preform consists of a wall formed by a multitude ofshort lengths of fibers randomly oriented in the wall and bonded by asettable resin which holds thefibers together but which does not fillthe voids between the fibers.

One method of forming a preform which is particularly suited tocommercial production involves the step of providing a perforated formwhich is rotated about its longitudinal axis while a vacuum is appliedinternally. A fiber chopper cuts a continuous strand offiber-reinforcing material, such as a glass fiber filament, into shortlengths and directs the chopped fibers toward the rotating fonn. Thevacuum applied to the perforated form causes the fibers to be laid up onthe form in a random manner. A settable binder resin is sprayed onto thefibers as they are deposited on the form. The vacuum applied to theperforated form, the amount of resin spray, and the amount of fibersdeposited on the form may be controlled so that the preform is formedinitially to have a configuration generally similar ,to the interiorcavity of the mold.

After the binder is cured, the prefonn is removed from the form and isthen inserted into the mold and compressed against the inner surfaces ofthe mold by expanding an inflatable bag within the preform. A settableresin is then caused to flow through the preform and the resin issubsequently cured. A more detailed description of the prefonnfabrication technique is generally set forth in the copendingapplication of Arthur J. Wiltshire et al., Ser. No. 742,692 filed July 5i968. When fiber-reinforced plastic articles are fabricated in thismanner, the preform must be formed so as to satisfy rigorous dimensionrequirements. In particular, the exterior dimensions of the preform mustbe substantially equal to the interior dimensions of the mold and liewithin a narrow tolerance range.

If the preform is oversized, it cannot be inserted into the mold andmust be discarded. There is no economical way to reshape the prefonn,nor is there a method of salvaging the materials forming the preform.Consequently, valuable production time and materials are lost.

If the preform's exterior dimensions are substantially equal to theinterior dimensions of the mold, the preform may be carefully insertedinto the mold. Since the exterior surface of the preform may bedisrupted or torn during the inserting process, an experiencedassemblyman is required to carefully position the preform in the mold.Consequently, in this instance, the preform inserting process is slowand requires a skilled assemblymans services. In addition, there stillexists the possibility that the preform may be torn during the processso as to render it unusable.

The difiiculties encountered in forming a preform with exteriordimensions substantially equal to the interior dimensions of theinterior of the mold may be fully appreciated when considered in view ofthe preform fabrication techniquedepositing fibers on a rotating formand spraying the deposited fibers with a resin binder. Consequently, theexterior preform dimensions are a function of several independentvariables none of which readily lend themselves to precise dimensionalcontrol. This is especially critical in view of the fact that a typicalmold having an 8.275 inch diameter has a tolerance of 0 to +0.005 inch.

Although it is desirable to form the preform with exterior dimensionssubstantially equal to the interior dimensions of the mold so as toprovide a minimum of clearance, several additional fabrication problemsarise if the preform is undersized. For example, if the preform is infact too small, it may split when the inflatable bag is inserted intothe preform and expanded so as to compress the preform against the innersurfaces of the mold. Consequently, the final product will not befiber-reinforced in the area of the split and a weak point may exist inthe structure so as to render the product unusable. In addition, if thepreform is undersized but does not split when subjected to internal bagpressure, a second structural defect may arise which will also renderthe final product useless. In this instance, the undersized preformfails to uniformly contact the inner surfaces of the mold when bagpressure is applied and resin-rich localized areas at the exteriorsurface of the final product result. The resin-rich areas will not beadequately fiber-reinforced, and the final product may have a tendencyto crack in these areas.

Consequently, according to the methods of the prior art, it wasconsidered necessary that the exterior dimensions of the preform besubstantially equal to the interior dimensions of the mold and be withina narrow tolerance range. However, the maintenance of this narrowtolerance range is extremely difiicult in view of the preformfabrication technique and the nebulous value of the maximum amount ofacceptable clearance.

SUMMARY OF THE INVENTION The present invention provides a method and anassembly for inserting a flexible, oversized preform into a hollow mold.According to the present invention, the cross sectional size of thepreform is temporarily reduced so that it may be easily inserted intothe mold. This reduction in the cross sectional size of the preform isprovided by forming an inwardly projecting furrow in the preform toreduce the cross sectional size of the preform by gathering portions ofthe preform into the furrow.

The present invention also provides an assembly for inserting theflexible, oversized preform into the mold. The assembly includes aninserting mandrel which has exterior dimensions less than the interiordimensions of the mold and the hollow preform so that the mandrel mayfit within the preform. According to the preferred embodiment of thepresent invention, the mandrel provides an aperture extending along itsouter peripheral surface. The assembly also includes a paddledimensioned to coact in sliding relationship with the aperture of theinserting mandrel. The paddle provides a surface which projects towardsthe aperture. The paddle is positioned adjacent to the open end of thehollow mold and along the interior surface of the mold. The preform ispositioned over the inserting mandrel and inserted into the mold so thatthe aperture of the inserting mandrel and the paddle are aligned. Thepreform will lie intermediate the aperture of the mandrel and thepaddle, which coact so as to form an inwardly extending furrow in thepreform as it is inserted into the mold. In this manner, the crosssectional size of the preform is temporarily reduced so that it will fitinto the mold. The inserting mandrel and the paddle may then bewithdrawn from the mold. An inflatable bag is then inserted within thepreform and inflated so as to force the preform against the interiorsurface of the mold. The subsequent molding operations as describedabove may then be performed.

The method of the present invention eliminates the problems existing inthe prior art which are indicated above.

described above. As there noted, the preform is formed by Initially, itmay be noted that the tolerance range with respect to preform size issubstantially increased. This is true since the upper limit of thetolerance rangeis no longer limited or fixed by the interior size of themold. Consequently, many of the preforms which were formerly rejected asbeing'oversized may beused to form satisfactory endproducts.

Since the upper limit of the tolerance size range of preforms sembly'ofthe present invention is'employed, the preform mayv be quickly andaccurately positioned inside the mold. As a result, the preforminserting process will entail a minimum of production time and will notrequire the services of a skilled assemblyman. I v Other advantages ofthis invention will become apparent from the following detaileddescription and the accompanying drawings.

BRIEFDESCRIPTIONAOF THE DRAWINGS FIG. 1 is' a perspective view of aninserting mandrel. and a paddle according to the present invention;

FIG. 2 is a composite sectional side view of the assembly shown in FIG-1, a mold,'and apreform; and,

FIG. 3 is a sectional view, the plane of the section being indicated bythe line 3-3 in FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS w FIGS 1 illustrates the preferredembodiment of an assembly whichis'useful ininserting an oversizedpreform into a hollow mold. This assembly. is particularly adapted forthe manufacture of tanks of the type often used for water sofieners orthe like-The illustrated assembly includes a hollow inserting mandrel.10 and a paddle l2. The inserting mandrel 10 includes a drical portion14 there are mandrel support guides-22 and 24 which project radiallyoutward. The mandrel support guides provide the cylindrical portion 14with a radial dimension at the plane of the aperture substantially equalto the exterior radiahdimension of the forward end 18. Therefore, theaperture 20 is definedby coplanar edges 22a and 24a of the man-. I

drel support guides 22 and 24 along the cylindrical portion 14 of theinserting mandrel and. the forward edge of the aperture is defined bythe edge 26 of the forward end face 18. It should be noted that. theaperture 20 may be fonned merely by a relievedportion in theexteriorperipheral surface of the cylindricalportion l4 and the forward end 18may have peripheral dimensions similar to those of the aperture 20.

The paddle 12 is provided with peripheral dimensions that substantiallymate with the aperture 20. In the embodiment illustrated in FIG. 1, thepaddle 12 has a substantially rectangu-- lar shape andprovides anarcuate projecting surface 28. The projecting surface 28 extends towardsthe aperture 20 when the paddle and the inserting mandrel are employedin accordance with themethodof this invention. The paddle 12 may. havean axial length which is equal to about one-half to g aboutthree-fourths of the axial length of the aperture 20.

FIG. 2 illustrates a hollow preform 30 positioned in a mold 32 by theassembly shown in FIG. 1. The mold-32 has a cylindricalportion.34-extending to an open rearward end 38and a closedforward end36. The preform 30 has a similar configu ration and is comprised of acylindrical portion 33 extending to a closed forward end 31 and an openrearward end 35.

In the method of the present invention, the preform 30 is initiallypositioned over the inserting mandrel 10 since the inserting mandrel hasexterior dimensions less than the interior dimensions of the preform.The paddle 12 is positioned inside the mold 32 adjacent tothe open end38. To this end, the paddle 12 is provided with a handle 40 whichisformed to clip over the open end 38 of the mold so as to securelyposition the paddle.

The inserting mandrel 10, with the preform 30 positioned over it, isthen inserted into the mold. A handle 42 is provided.

intermediate the inserting mandrel l0 andthe paddle 12, is in sertedinto the mold, the aperture 20 and the projecting surface 28 form aninwardly extending furrow 44 in the preform. As shown in FIG. 2,1thepreform 30 has been completely inserted into the mold and the furrow 44has been formed in the preform. The furrow axially extends alongsubstantially the entire axial length of the cylindrical portion 33 ofthe preform 30.

As best shown in FIG. 3, the furrow 44 reduces the cross sectional sizeof the preform 30 by gathering portions of the preform material. Toeffect this gathering of preform material, the insertingmandrel l0 andthe paddle 12 provide an increased circumferential path about which thepreform musttravel and a localized area where the excess preformmaterial is accumulated.

Once the preform 30 has been properly positioned in the mold 32, theinserting mandrel 10 may be withdrawn from the mold by means of thehandle 42.

Once the inserting mandrel and the paddle have been removed from themold, the inflatable bag may be inserted into the preform and inflatedso as to compress the preform against the inner surfaces of the mold.The furrow 44 which was formed in the preform will alsobe compressed andthe portions of the preform formerly gathered in the furrow will beuniformly distributed throughout the preform. Consequently, the preformwill be compressed. uniformly against the inner surfaces of the moldandthe subsequent molding steps, described above, may b'eperformed. v

When the method of the present invention is employed as described above,the preform does not have to be initially. formed so as to satisfy therigorous dimensional requirements imposed by the prior art techniques.In particular, the maximum interior mold dimensions do not limit theexterior dimensions of the preform and an oversizedprefonn is no longerdiscarded as unusable. For example, when the method of the presentinvention is employed, a preform having an outside diarneter 0.020 inchgreater than the inside diameter of the mold is easily inserted into themold and is usable. In effect, the upper limit of thenarrow tolerancerange of the prior art methods has been increased.

Sincethe exterior dimensions of the preform do not have to besubstantially equal to the interior dimensions of the mold when themethod of the present invention is employed, an experienced assemblymanis no longer required to carefully'insert the preform into the moldwithout tearing or disrupting the exterior surface of the preform. Infact, when the method and assembly of the present invention areutilized, an inexperienced assemblyman is able to quickly and correctlyinsert the preform into the mold. Since the assembly of the presentinvention fits the preform to the mold as it is being inserted,production time is not wasted in a tedious fitting process.

The prior art problemswith respect to the degree. which the preformcould be undersized or the amount of acceptable clearance between; thepreform and the mold are also tially avoided. In particular, the preformwill not tend to split.

as the inflatable bag compresses it against the inner surfaces of themold, since the exterior dimensions of the prefonn are actually greaterthan the interior dimensions of the mold. in addition, the final productwill not tend to have resin-rich areas at its exterior surface, sincesufiicient fiber-reinforcing materials are provided by the oversizedpreform.

The assembly of the present invention also radially aligns the preformwithin the mold as it is inserted. The mandrel support guides 22 and 24provide the cylindrical portion 14 of the inserting mandrel with aradial dimension equal to that of the expanded forward end 18. Thus, thesupport guides 22 and 24 and the forward end 18 provide a coplanarsupport surface for the inserting mandrel. The support guides and theforward end may be appropriately dimensioned so as to radially align themandrel and the preform within the mold. This feature of the presentinvention is best illustrated in FIG. 3.

In addition, the end face 18 of the inserting mandrel is provided withapertures 46, 48, and 50 which permit the free passage of air. Theseapertures permit air to escape from the -mold, throughthe preform lyingintermediate the mold and the forward end, as the preform is inserted,and prevent the formation of a vacuum as the inserting mandrel iswithdrawn from the preform.

Although a preferred embodiment of this invention is illustrated, it isto be understood that various modifications and rearrangements of partsmay be resorted to without departing from the scope of the invention.

What is claimed is:

l.\ A method of inserting an oversized flexible preform into an openingin a hollow mold to lay up the preform against the inner surface of themold, comprising the steps of providing mandrel means and paddle means,positioning said preform around said mandrel means, positioning saidpaddle means within said mold, inserting said mandrel means and preforminto said mold and deflectingly engaging said preform between saidmandrel and paddle means within said mold to thereby temporarily form atleast one inwardly projecting furrow along said preform so as to reducethe cross sectional size of said preform so that said oversized preformfits said mold.

2. A method in accordance with claim 1, wherein said preform is formedof a fibrous material.

3. A method in accordance with claim 1, wherein the step of deflectinglyengaging said preform includes providing support for maintaining saidfurrow in said preform along a substantial extent of the longitudinallength of said preform.

4. A method in accordance with claim 3, wherein said oversized preformis substantially cylindrical and has a closed forward end and saidmandrel means includes a forward end dimensioned to press against saidclosed forward end of said preform during the step of inserting saidmandrel means and preform into said mold.

5. A method in accordance with claim 4, wherein said furrow extendssubstantially axially along said oversized preform.

6. A method in accordance with claim 4 wherein the step of providingsupport for maintaining said furrow includes constraining said preformalong a radially, inwardly projecting surface provided by said paddlemeans adjacent a recess provided by said mandrel means.

7. A method of inserting an oversized flexible preform into an openingin a hollow mold to lay up the preform against the inner surface of themold, comprising the steps of providing a flexible preform having acylindrical sidewall and a closed end, providing a mold having a moldcavity adapted to receive said preform, inserting said preform into saidcavity by applying axial pressure to said closed end, while saidpressure is applied, applying inwardly directed radial pressure to alongitudinal portion of the cylindrical sidewall within the mold cavityto reduce the circumference of said sidewall, maintaining said pressurealong a substantial extent of said longitudinal portion until saidpreform is fully received in said mold cavity to thereby maintain areduced preform circumference during and after preform insertion,removing said inwardly directed radial pressure, and then forcing allportions of said cylindrical sidewall against said mold cavity

1. A method of inserting an oversized flexible preform into an openingin a hollow mold to lay up the preform against the inner surface of themold, comprising the steps of providing mandrel means and paddle means,positioning said preform around said mandrel means, positioning saidpaddle means within said mold, inserting said mandrel means and preforminto said mold and deflectingly engaging said preform between saidmandrel and paddle means within said mold to thereby temporarily form atleast one inwardly projecting furrow along said preform so as to reducethe cross sectional size of said preform so that said oversized preformfits said mold.
 2. A method in accordance with claim 1, wherein saidpreform is formed of a fibrous material.
 3. A method in accordance withclaim 1, wherein the step of deflectingly engaging said preform includesproviding support for maintaining said furrow in said preform along asubstantiAl extent of the longitudinal length of said preform.
 4. Amethod in accordance with claim 3, wherein said oversized preform issubstantially cylindrical and has a closed forward end and said mandrelmeans includes a forward end dimensioned to press against said closedforward end of said preform during the step of inserting said mandrelmeans and preform into said mold.
 5. A method in accordance with claim4, wherein said furrow extends substantially axially along saidoversized preform.
 6. A method in accordance with claim 4 wherein thestep of providing support for maintaining said furrow includesconstraining said preform along a radially, inwardly projecting surfaceprovided by said paddle means adjacent a recess provided by said mandrelmeans.
 7. A method of inserting an oversized flexible preform into anopening in a hollow mold to lay up the preform against the inner surfaceof the mold, comprising the steps of providing a flexible preform havinga cylindrical sidewall and a closed end, providing a mold having a moldcavity adapted to receive said preform, inserting said preform into saidcavity by applying axial pressure to said closed end, while saidpressure is applied, applying inwardly directed radial pressure to alongitudinal portion of the cylindrical sidewall within the mold cavityto reduce the circumference of said sidewall, maintaining said pressurealong a substantial extent of said longitudinal portion until saidpreform is fully received in said mold cavity to thereby maintain areduced preform circumference during and after preform insertion,removing said inwardly directed radial pressure, and then forcing allportions of said cylindrical sidewall against said mold cavity.